In an optical fiber communications system, an optic device is currently applied, light path filtering parts of which are all designed in a wave plate manner. As shown in FIG. 1, the optic device includes a laser emitter 11, a first wave plate 12, a detector 13, a second wave plate 14 and an optical fiber adapter 15. A central axis 16-1 of an emitting end of the laser emitter 11 and a central axis 16-2 of a receiving end of the optical fiber adapter 15 are parallel to each other, but are not coincident. The first wave plate 12 is disposed between the laser emitter 11 and the optical fiber adapter 15, and an angle is between the first wave plate 12 and the emitting end of the laser emitter 11 and between the first wave plate 12 and the receiving end of the optical fiber adapter 15. The second wave plate 14 disposed parallel to a receiving end of the detector 13 is a filter, and filters optical signals that are from the optical fiber adapter 15 and are reflected by the first wave plate 12, and after the optical signals from the optical fiber adapter 15 pass through the second wave plate 14, some of the optical signals pass through the receiving end of the detector 13 and enter the detector 13.
As shown in FIG. 2, optical signals emitted by the laser emitter include a central axis ray 21, an edge ray 22 and an edge ray 23, where the edge ray 22 and the edge ray 23 are symmetrical relative to the central axis ray 21. An angle between a light path of the optical signals emitted by the laser emitter and an optical axis 24-1 of a wave plate 24 is 45 degrees, and therefore when the central axis ray 21 of the optical signals is incident at 45 degrees relative to the wave plate 24, the edge ray 22 and the edge ray 23 separately have different incident angles relative to the optical axis 24-1 of the wave plate 24, where an incident angle of the edge ray 22 relative to the optical axis 24-1 of the wave plate 24 is θ1, an incident angle of the edge ray 23 relative to the optical axis 24-1 of the wave plate 24 is θ2, and θ1≠θ2.
According to the light refraction law, incident angles of the central axis ray 21, the edge ray 22 and the edge ray 23 relative to the optical axis 24-1 of the wave plate 24 are 45 degrees, θ1 and θ2 respectively, and the wave plate 24 has a same refraction index, and therefore after the central axis ray 21, the edge ray 22 and the edge ray 23 are emitted from the wave plate 24, different refraction angles are separately generated, where a refraction angle generated after the edge ray 22 passes through the wave plate 24 is maximum, a refraction angle generated after the edge ray 23 passes through the wave plate 24 is minimum, and a refraction angle generated after the central axis ray 21 passes through the wave plate 24 is between the refraction angle generated after the edge ray 22 passes through the wave plate 24 and the refraction angle generated after the edge ray 23 passes through the wave plate 24. The refraction angle generated after the edge ray 22 passes through the wave plate 24 and the refraction angle generated after the edge ray 23 passes through the wave plate 24 are different, and therefore a ray generated after the edge ray 22 passes through the wave plate 24, and a ray generated after the edge ray 23 passes through the wave plate 24 and a ray generated after the central axis ray 21 passes through the wave plate 24 are not symmetrical. Therefore, the central axis ray 21, the edge ray 22 and the edge ray 23 cannot converge to a same point of a central optical axis at a focal point of a receiving end of an optical fiber adapter, and what are shown by 25 in FIG. 2 are focal points in which dislocation occurs.
In the existing technology, when a light beam passes through a wave plate disposed between a laser emitter and an optical fiber adapter, and then forms a converged light spot, because edge rays at two sides of a central axis ray have different refraction angles after passing through the wave plate, focal points of the edge rays at the two sides cannot converge to a point with that of the central axis ray, a focal spot is formed, thereby affecting efficiency of coupling optical signals.